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Hello all,
I am currently working on a game engine for use with my game development that I would like to be as flexible as possible. As such the exact requirements for how things should work can't be nailed down to a specific implementation and I am looking for, at least now, a default good average case scenario design.
Here is what I have implemented:
Deferred rendering using OpenGL
Arbitrary number of lights and shadow mapping
Each rendered object, as defined by a set of geometry, textures, animation data, and a model matrix is rendered with its own draw call
Skeletal animations implemented on the GPU.
Model matrix transformation implemented on the GPU
Frustum and octree culling for optimization
Here are my questions and concerns:
Doing the skeletal animation on the GPU, currently, requires doing the skinning for each object multiple times per frame: once for the initial geometry rendering and once for the shadow map rendering for each light for which it is not culled. This seems very inefficient. Is there a way to do skeletal animation on the GPU only once across these render calls?
Without doing the model matrix transformation on the CPU, I fail to see how I can easily batch objects with the same textures and shaders in a single draw call without passing a ton of matrix data to the GPU (an array of model matrices then an index for each vertex into that array for transformation purposes?)
If I do the matrix transformations on the CPU, It seems I can't really do the skinning on the GPU as the pre-transformed vertexes will wreck havoc with the calculations, so this seems not viable unless I am missing something
Overall it seems like simplest solution is to just do all of the vertex manipulation on the CPU and pass the pre-transformed data to the GPU, using vertex shaders that do basically nothing. This doesn't seem the most efficient use of the graphics hardware, but could potentially reduce the number of draw calls needed.

Really, I am looking for some advice on how to proceed with this, how something like this is typically handled. Are the multiple draw calls and skinning calculations not a huge deal? I would LIKE to save as much of the CPU's time per frame so it can be tasked with other things, as to keep CPU resources open to the implementation of the engine. However, that becomes a moot point if the GPU becomes a bottleneck.

Hello!
I would like to introduce Diligent Engine, a project that I've been recently working on. Diligent Engine is a light-weight cross-platform abstraction layer between the application and the platform-specific graphics API. Its main goal is to take advantages of the next-generation APIs such as Direct3D12 and Vulkan, but at the same time provide support for older platforms via Direct3D11, OpenGL and OpenGLES. Diligent Engine exposes common front-end for all supported platforms and provides interoperability with underlying native API. Shader source code converter allows shaders authored in HLSL to be translated to GLSL and used on all platforms. Diligent Engine supports integration with Unity and is designed to be used as a graphics subsystem in a standalone game engine, Unity native plugin or any other 3D application. It is distributed under Apache 2.0 license and is free to use. Full source code is available for download on GitHub.
Features:
True cross-platform
Exact same client code for all supported platforms and rendering backends
No #if defined(_WIN32) ... #elif defined(LINUX) ... #elif defined(ANDROID) ...
No #if defined(D3D11) ... #elif defined(D3D12) ... #elif defined(OPENGL) ...
Exact same HLSL shaders run on all platforms and all backends
Modular design
Components are clearly separated logically and physically and can be used as needed
Only take what you need for your project (do not want to keep samples and tutorials in your codebase? Simply remove Samples submodule. Only need core functionality? Use only Core submodule)
No 15000 lines-of-code files
Clear object-based interface
No global states
Key graphics features:
Automatic shader resource binding designed to leverage the next-generation rendering APIs
Multithreaded command buffer generation
50,000 draw calls at 300 fps with D3D12 backend
Descriptor, memory and resource state management
Modern c++ features to make code fast and reliable
The following platforms and low-level APIs are currently supported:
Windows Desktop: Direct3D11, Direct3D12, OpenGL
Universal Windows: Direct3D11, Direct3D12
Linux: OpenGL
Android: OpenGLES
MacOS: OpenGL
iOS: OpenGLES
API Basics
Initialization
The engine can perform initialization of the API or attach to already existing D3D11/D3D12 device or OpenGL/GLES context. For instance, the following code shows how the engine can be initialized in D3D12 mode:
#include "RenderDeviceFactoryD3D12.h"
using namespace Diligent;
// ...
GetEngineFactoryD3D12Type GetEngineFactoryD3D12 = nullptr;
// Load the dll and import GetEngineFactoryD3D12() function
LoadGraphicsEngineD3D12(GetEngineFactoryD3D12);
auto *pFactoryD3D11 = GetEngineFactoryD3D12();
EngineD3D12Attribs EngD3D12Attribs;
EngD3D12Attribs.CPUDescriptorHeapAllocationSize[0] = 1024;
EngD3D12Attribs.CPUDescriptorHeapAllocationSize[1] = 32;
EngD3D12Attribs.CPUDescriptorHeapAllocationSize[2] = 16;
EngD3D12Attribs.CPUDescriptorHeapAllocationSize[3] = 16;
EngD3D12Attribs.NumCommandsToFlushCmdList = 64;
RefCntAutoPtr<IRenderDevice> pRenderDevice;
RefCntAutoPtr<IDeviceContext> pImmediateContext;
SwapChainDesc SwapChainDesc;
RefCntAutoPtr<ISwapChain> pSwapChain;
pFactoryD3D11->CreateDeviceAndContextsD3D12( EngD3D12Attribs, &pRenderDevice,
&pImmediateContext, 0 );
pFactoryD3D11->CreateSwapChainD3D12( pRenderDevice, pImmediateContext, SwapChainDesc,
hWnd, &pSwapChain );
Creating Resources
Device resources are created by the render device. The two main resource types are buffers, which represent linear memory, and textures, which use memory layouts optimized for fast filtering. To create a buffer, you need to populate BufferDesc structure and call IRenderDevice::CreateBuffer(). The following code creates a uniform (constant) buffer:
BufferDesc BuffDesc;
BufferDesc.Name = "Uniform buffer";
BuffDesc.BindFlags = BIND_UNIFORM_BUFFER;
BuffDesc.Usage = USAGE_DYNAMIC;
BuffDesc.uiSizeInBytes = sizeof(ShaderConstants);
BuffDesc.CPUAccessFlags = CPU_ACCESS_WRITE;
m_pDevice->CreateBuffer( BuffDesc, BufferData(), &m_pConstantBuffer );
Similar, to create a texture, populate TextureDesc structure and call IRenderDevice::CreateTexture() as in the following example:
TextureDesc TexDesc;
TexDesc.Name = "My texture 2D";
TexDesc.Type = TEXTURE_TYPE_2D;
TexDesc.Width = 1024;
TexDesc.Height = 1024;
TexDesc.Format = TEX_FORMAT_RGBA8_UNORM;
TexDesc.Usage = USAGE_DEFAULT;
TexDesc.BindFlags = BIND_SHADER_RESOURCE | BIND_RENDER_TARGET | BIND_UNORDERED_ACCESS;
TexDesc.Name = "Sample 2D Texture";
m_pRenderDevice->CreateTexture( TexDesc, TextureData(), &m_pTestTex );
Initializing Pipeline State
Diligent Engine follows Direct3D12 style to configure the graphics/compute pipeline. One big Pipelines State Object (PSO) encompasses all required states (all shader stages, input layout description, depth stencil, rasterizer and blend state descriptions etc.)
Creating Shaders
To create a shader, populate ShaderCreationAttribs structure. An important member is ShaderCreationAttribs::SourceLanguage. The following are valid values for this member:
SHADER_SOURCE_LANGUAGE_DEFAULT - The shader source format matches the underlying graphics API: HLSL for D3D11 or D3D12 mode, and GLSL for OpenGL and OpenGLES modes.
SHADER_SOURCE_LANGUAGE_HLSL - The shader source is in HLSL. For OpenGL and OpenGLES modes, the source code will be converted to GLSL. See shader converter for details.
SHADER_SOURCE_LANGUAGE_GLSL - The shader source is in GLSL. There is currently no GLSL to HLSL converter.
To allow grouping of resources based on the frequency of expected change, Diligent Engine introduces classification of shader variables:
Static variables (SHADER_VARIABLE_TYPE_STATIC) are variables that are expected to be set only once. They may not be changed once a resource is bound to the variable. Such variables are intended to hold global constants such as camera attributes or global light attributes constant buffers.
Mutable variables (SHADER_VARIABLE_TYPE_MUTABLE) define resources that are expected to change on a per-material frequency. Examples may include diffuse textures, normal maps etc.
Dynamic variables (SHADER_VARIABLE_TYPE_DYNAMIC) are expected to change frequently and randomly.
This post describes the resource binding model in Diligent Engine.
The following is an example of shader initialization:
ShaderCreationAttribs Attrs;
Attrs.Desc.Name = "MyPixelShader";
Attrs.FilePath = "MyShaderFile.fx";
Attrs.SearchDirectories = "shaders;shaders\\inc;";
Attrs.EntryPoint = "MyPixelShader";
Attrs.Desc.ShaderType = SHADER_TYPE_PIXEL;
Attrs.SourceLanguage = SHADER_SOURCE_LANGUAGE_HLSL;
BasicShaderSourceStreamFactory BasicSSSFactory(Attrs.SearchDirectories);
Attrs.pShaderSourceStreamFactory = &BasicSSSFactory;
ShaderVariableDesc ShaderVars[] =
{
{"g_StaticTexture", SHADER_VARIABLE_TYPE_STATIC},
{"g_MutableTexture", SHADER_VARIABLE_TYPE_MUTABLE},
{"g_DynamicTexture", SHADER_VARIABLE_TYPE_DYNAMIC}
};
Attrs.Desc.VariableDesc = ShaderVars;
Attrs.Desc.NumVariables = _countof(ShaderVars);
Attrs.Desc.DefaultVariableType = SHADER_VARIABLE_TYPE_STATIC;
StaticSamplerDesc StaticSampler;
StaticSampler.Desc.MinFilter = FILTER_TYPE_LINEAR;
StaticSampler.Desc.MagFilter = FILTER_TYPE_LINEAR;
StaticSampler.Desc.MipFilter = FILTER_TYPE_LINEAR;
StaticSampler.TextureName = "g_MutableTexture";
Attrs.Desc.NumStaticSamplers = 1;
Attrs.Desc.StaticSamplers = &StaticSampler;
ShaderMacroHelper Macros;
Macros.AddShaderMacro("USE_SHADOWS", 1);
Macros.AddShaderMacro("NUM_SHADOW_SAMPLES", 4);
Macros.Finalize();
Attrs.Macros = Macros;
RefCntAutoPtr<IShader> pShader;
m_pDevice->CreateShader( Attrs, &pShader );
Creating the Pipeline State Object
To create a pipeline state object, define instance of PipelineStateDesc structure. The structure defines the pipeline specifics such as if the pipeline is a compute pipeline, number and format of render targets as well as depth-stencil format:
// This is a graphics pipeline
PSODesc.IsComputePipeline = false;
PSODesc.GraphicsPipeline.NumRenderTargets = 1;
PSODesc.GraphicsPipeline.RTVFormats[0] = TEX_FORMAT_RGBA8_UNORM_SRGB;
PSODesc.GraphicsPipeline.DSVFormat = TEX_FORMAT_D32_FLOAT;
The structure also defines depth-stencil, rasterizer, blend state, input layout and other parameters. For instance, rasterizer state can be defined as in the code snippet below:
// Init rasterizer state
RasterizerStateDesc &RasterizerDesc = PSODesc.GraphicsPipeline.RasterizerDesc;
RasterizerDesc.FillMode = FILL_MODE_SOLID;
RasterizerDesc.CullMode = CULL_MODE_NONE;
RasterizerDesc.FrontCounterClockwise = True;
RasterizerDesc.ScissorEnable = True;
//RSDesc.MultisampleEnable = false; // do not allow msaa (fonts would be degraded)
RasterizerDesc.AntialiasedLineEnable = False;
When all fields are populated, call IRenderDevice::CreatePipelineState() to create the PSO:
m_pDev->CreatePipelineState(PSODesc, &m_pPSO);
Binding Shader Resources
Shader resource binding in Diligent Engine is based on grouping variables in 3 different groups (static, mutable and dynamic). Static variables are variables that are expected to be set only once. They may not be changed once a resource is bound to the variable. Such variables are intended to hold global constants such as camera attributes or global light attributes constant buffers. They are bound directly to the shader object:

PixelShader->GetShaderVariable( "g_tex2DShadowMap" )->Set( pShadowMapSRV );
Mutable and dynamic variables are bound via a new object called Shader Resource Binding (SRB), which is created by the pipeline state:
m_pPSO->CreateShaderResourceBinding(&m_pSRB);
Dynamic and mutable resources are then bound through SRB object:
m_pSRB->GetVariable(SHADER_TYPE_VERTEX, "tex2DDiffuse")->Set(pDiffuseTexSRV);
m_pSRB->GetVariable(SHADER_TYPE_VERTEX, "cbRandomAttribs")->Set(pRandomAttrsCB);
The difference between mutable and dynamic resources is that mutable ones can only be set once for every instance of a shader resource binding. Dynamic resources can be set multiple times. It is important to properly set the variable type as this may affect performance. Static variables are generally most efficient, followed by mutable. Dynamic variables are most expensive from performance point of view. This post explains shader resource binding in more details.
Setting the Pipeline State and Invoking Draw Command
Before any draw command can be invoked, all required vertex and index buffers as well as the pipeline state should be bound to the device context:
// Clear render target
const float zero[4] = {0, 0, 0, 0};
m_pContext->ClearRenderTarget(nullptr, zero);
// Set vertex and index buffers
IBuffer *buffer[] = {m_pVertexBuffer};
Uint32 offsets[] = {0};
Uint32 strides[] = {sizeof(MyVertex)};
m_pContext->SetVertexBuffers(0, 1, buffer, strides, offsets, SET_VERTEX_BUFFERS_FLAG_RESET);
m_pContext->SetIndexBuffer(m_pIndexBuffer, 0);
m_pContext->SetPipelineState(m_pPSO);
Also, all shader resources must be committed to the device context:
m_pContext->CommitShaderResources(m_pSRB, COMMIT_SHADER_RESOURCES_FLAG_TRANSITION_RESOURCES);
When all required states and resources are bound, IDeviceContext::Draw() can be used to execute draw command or IDeviceContext::DispatchCompute() can be used to execute compute command. Note that for a draw command, graphics pipeline must be bound, and for dispatch command, compute pipeline must be bound. Draw() takes DrawAttribs structure as an argument. The structure members define all attributes required to perform the command (primitive topology, number of vertices or indices, if draw call is indexed or not, if draw call is instanced or not, if draw call is indirect or not, etc.). For example:
DrawAttribs attrs;
attrs.IsIndexed = true;
attrs.IndexType = VT_UINT16;
attrs.NumIndices = 36;
attrs.Topology = PRIMITIVE_TOPOLOGY_TRIANGLE_LIST;
pContext->Draw(attrs);
Tutorials and Samples
The GitHub repository contains a number of tutorials and sample applications that demonstrate the API usage.
Tutorial 01 - Hello Triangle
This tutorial shows how to render a simple triangle using Diligent Engine API.
Tutorial 02 - Cube
This tutorial demonstrates how to render an actual 3D object, a cube. It shows how to load shaders from files, create and use vertex, index and uniform buffers.
Tutorial 03 - Texturing
This tutorial demonstrates how to apply a texture to a 3D object. It shows how to load a texture from file, create shader resource binding object and how to sample a texture in the shader.
Tutorial 04 - Instancing
This tutorial demonstrates how to use instancing to render multiple copies of one object using unique transformation matrix for every copy.
Tutorial 05 - Texture Array
This tutorial demonstrates how to combine instancing with texture arrays to use unique texture for every instance.
Tutorial 06 - Multithreading
This tutorial shows how to generate command lists in parallel from multiple threads.
Tutorial 07 - Geometry Shader
This tutorial shows how to use geometry shader to render smooth wireframe.
Tutorial 08 - Tessellation
This tutorial shows how to use hardware tessellation to implement simple adaptive terrain rendering algorithm.
Tutorial_09 - Quads
This tutorial shows how to render multiple 2D quads, frequently swithcing textures and blend modes.

AntTweakBar sample demonstrates how to use AntTweakBar library to create simple user interface.

Atmospheric scattering sample is a more advanced example. It demonstrates how Diligent Engine can be used to implement various rendering tasks: loading textures from files, using complex shaders, rendering to textures, using compute shaders and unordered access views, etc.

The repository includes Asteroids performance benchmark based on this demo developed by Intel. It renders 50,000 unique textured asteroids and lets compare performance of D3D11 and D3D12 implementations. Every asteroid is a combination of one of 1000 unique meshes and one of 10 unique textures.

Integration with Unity
Diligent Engine supports integration with Unity through Unity low-level native plugin interface. The engine relies on Native API Interoperability to attach to the graphics API initialized by Unity. After Diligent Engine device and context are created, they can be used us usual to create resources and issue rendering commands. GhostCubePlugin shows an example how Diligent Engine can be used to render a ghost cube only visible as a reflection in a mirror.

I'm trying to load data from a .gltf file into a struct to use to load a .bin file. I don't think there is a problem with how the vertex positions are loaded, but with the indices. This is what I get when drawing with glDrawArrays(GL_LINES, ...):

I am somewhat new to game development and trying to create a basic 3d engine. I have managed to set up a first person camera and it seems to be working fine for the most part. While I am able to look up, down, left and right just fine the camera is constrained to the mouse movement in the window (i.e when the mouse reaches edges of the window it discontinues camera rotation and mouse is out of window bounds. I tried to use SDL_WarpMouseInWindow(window, center.x,center.y) but when I do this then it messes up the camera and the camera is stuck, even though there is some slight movement of the camera, it keeps going back to the center.
void Camera::UpdateViewByMouse(SDL_Window &window, glm::vec2 mousePosition)
{
float xDistanceFromWindowCenter = mousePosition.x - ((float)1024 / 2) ;
float yDistanceFromWindowCenter = ((float)720 / 2) - mousePosition.y;
yaw = xDistanceFromWindowCenter * cameraRotationSpeed;
pitch = yDistanceFromWindowCenter * cameraRotationSpeed;
SDL_WarpMouseInWindow(&window, 1024 / 2, 768 / 2);
}
i’ve been stuck on this for far too long. any help would be much appreciated
i have also tried relative mouse movement, and .xrel and .yrel to avail. polling mouse state with sdl_event. I do also know that SDL_WarpMouseInWindow makes change to event and have tried also ignore and reenabling to no avail

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I wish to have shadows with multiple lights. Each light's shadow rendered to a depth cubemap. How do I render each cubemap onto a single cubemap with transparency so have a cubemap with all the shadows?

It's not clear what you want.

Shadow mapping works only for the single position of a single point light. You can not combine shadowmaps from multiple lights if they have different positions. (Cubemaps have 6 maps, but they are all relative to the same position.)

I wish to have shadows with multiple lights. Each light's shadow rendered to a depth cubemap. How do I render each cubemap onto a single cubemap with transparency so have a cubemap with all the shadows?

It's not clear what you want.

Shadow mapping works only for the single position of a single point light. You can not combine shadowmaps from multiple lights if they have different positions. (Cubemaps have 6 maps, but they are all relative to the same position.)

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You have one shadow map for each light and iterate over all potential lights affecting a pixel.

Directional and spotlights need only a single shadowmap.

Only lights shining in every direction need a cubemap (rarely used).

We still use a lot of lights that don't cast any shadow at all.

For your usecase you should also read about shadow volumes (used in Doom 3, uncommon today but very accurate. Frictional Games also released their older engine source for the game Pemumbra which used it too).

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You have one shadow map for each light and iterate over all potential lights affecting a pixel.

Directional and spotlights need only a single shadowmap.

Only lights shining in every direction need a cubemap (rarely used).

We still use a lot of lights that don't cast any shadow at all.

For your usecase you should also read about shadow volumes (used in Doom 3, uncommon today but very accurate. Frictional Games also released their older engine source for the game Pemumbra which used it too).

Thanks, I've looked into shadow volumes but can't find an example I can use for multi lighting.

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Try shadow maps first, and only if it does not work look for shadow volumes.

I expected a problem with portals and shadow maps, but after thinking of it i guess i'm just wrong and shadow maps will work as expected if you render them with geometry seen through portals.

There is no big difference between multiple lights or a single light with any method, so tutorials focus mostly only a single light.

It's always the same: You iterate over all lights, check shadow for each, sum up received light if unshadowed.

(There are methods that cluster multiple lights as an optimization, but that's not fundamental tech you want to start with)

How you do this iteration depends on rendering techniques (forward vs. deferred), but determinating if in shadow or not is pretty independent of that.

Start with a single light. After you have this add shadowing, and finally move on to multiple lights - no need to learn all at once.

Also notice that shadowing == determinating visibilty of the light source. And visibility is THE primary problem in computer graphics, so don't expect perfect results in one day ;)

I don't want to reinvent the wheel. Theres a book called opengl insights, chapter on multi lighting cubemaps with huge count. But it's for a version my laptop does not support, so ill have to buy a new pc.

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Starting with the basics is not reinventing. (IIRC you are the guy said being new to OpenGL?)

The problem is, it's still unclear what you want. I even looked up the Insights book - there is no chapter about cube map lighting. Only about generating multiple shadow maps 'at once' using geometry shaders.

You need to describe the algorithm - what does it achieve and how does it get there? (Or give a proper reference to the right book / paper / tutorial)

And what harware limitation has your laptop? There might be a way around...